Securing / Parking / Chocking 320 S on Inclined Home Driveway

@kvr99, welcome and congratulations on your trailer.  Something that provides friction between itself and your driveway is the answer. Off-hand, a house brick or paver would work. Others may have more pertinent suggestions. But, what a wonderful problem to solve. If you didn't have your t@b, this wouldn't be a concern. Enjoy your dilemma. It's all part of the adventure. Happy t@bbing!

Welcome @kvr99! I’d consider some heavy duty ridged rubber chocks like these. The reviews mention inclines on concrete surfaces. 

This would make a great little problem for a high school physics class.
Poly chocks will not provide adequate friction on an inclined paved (a presumably sealed) asphalt driveway. The bal leveler also does not seem like a good idea. Whatever you decide to use, what you are looking for is good friction on both wheels. Lifting one wheel a bit is unloading that wheel and overloading the opposite one. You want both wheels to share the load equally. So.... use rubberized chocks in lieu of poly. 
Once you are chocked and decoupled lower the trailer tongue as far as you can to reduce the moment and decrease the force on the tires. Make sure that both wheels share the load.  
You could use a wheel lock to keep the wheels from being able to turn. You still need to think about it sliding. Rain won't matter since the patch under the tires will stay dry. 
Don't rely on the trailer brakes since they won't hold after the battery drains.
Here is a style of rubberized chock to consider.   https://www.uline.com/Product/Detail/H-4193/Dock-and-Trailer-Equipment/Rubber-Wheel-Chocks-with-Handles-4-1-2-x-10-1-2-x-7?pricode=WA9682&gadtype=pla&id=H-4193&gclid=EAIaIQobChMI0OSd7_iX6gIVAYbICh32HQFHEAQYAyABEgKujfD_BwE&gclsrc=aw.ds
You will find other chocks available at Tractor Supply.

I second the Harbor Freight rubber chocks.  They are not very expensive.  If you find them on sale, or with one of their coupons they are cheaper still.

Agree with @DougH & @ADRawli, otherwise it's a no go.

Here's an example with the physics calculated, showing that a car parked in the rain on the 31-degree slope of a racetrack slope will slide down it (see example 5)..
http://faculty.mansfield.edu/hiseri/MA1135/1135L15.pdf
I've used the same coefficient of friction with a T@B weight of 2000 lbs at slopes between 10-15 degrees..

12° and 15° are a "no-go", as the downhill weight exceeds the weight required to overcome the friction of tires on pavement.  At 10°, the downhill weight is 348 lbs, but it would take more than 395 lbs to make it slide.  Still that's only a 45 lb margin.  At 11° of slope, it's even more iffy, as it would only take 11 lbs more of a push to start it sliding.  And this is based on locked wheels (like if you pulled the pin on the safety brake).  I expect a plastic chock to have even less friction than a rubber one might have.

Good for you, @kvr99, for asking the right question!
Apologies to those who hate trigonometry, but the math tells us this is a very risky situation, short of maybe attaching the Tab to a steel cable anchored in concrete.  Even then, I'm imagining that hitching & unhitching could be another difficult situation, not to mention the stress on hitch & TV components after repeatedly backing up on such an incline.  Is there even a suitable anchor point for a cable at the rear of the Tab?
I wonder what the steeper grades are on mountain roads.  I seem to recall seeing warning signs for some.  Maybe 9%?

Also, great idea by @Tampakayaker - dropping the jack post into a concrete hole would provide an added safety margin, though you'd need to keep an eye on its attachment bolts to the frame for any signs of stress.  

Update:  I have not verified the true coefficient of friction value asserted in the above example of car tires on wet asphalt, or whether that is really a static friction value as opposed to a dynamic one.  The following list of coefficient values for various materials lists a value of 0.72 for car tires on dry asphalt, for example, which would yield a much different result..  
www.engineeringtoolbox.com/amp/friction-coefficients-d_778.html

It's also apparent that various combinations of different (and even similar) materials can vary widely in their combined friction coefficients, and also depending on conditions such as wet/dry, rough/smooth, etc.  The only way to get a reliable coefficient value would be to test the actual materials by measuring how many pounds of force it would take to push the object (eg, a chocked T@B) on a similar but level surface (driveway), expressed as a fraction of its weight, then repeat the calculations above.

Sharon_is_SAM said:

How about putting a post in the ground with a 2 inch ball!

Ooooh.... I like that idea, but you’d still have to work out the logistics of how to get the hitch off the TV’s ball and onto the post’s ball without moving the trailer (which would be especially scary on a steep slope).  The idea of parking on slope that steep just seems to have many ‘watch outs’ no matter the solution.  It really depends on the true angle of the slope I guess.  <10% with quality chocks may be fine... but ~15%... yikes!   In lieu of a solid anchor point on both ends of any anchoring chain/strap, I think I’d be looking for another parking option.   

I have a 2018 320 CS-S parked on my driveway with an 8-10 degree slope (per an iphone app). I have the BAL leveler on one side (mostly correcting the 2.9 degree slope side to side) and a BAL locking chock on the other side. My driveway is concrete and we are in rainy oregon. Its been parked this way for about 6 weeks and I’m confident in the setup so far. The trailer does do an alarming little scoot when we pull it off the hitch, I think just on the locking chock side (the leveler side doesn’t seem to move at all) but it stops quickly. 

This article has an incredible photo of a jacked up trailer on a very steep driveway..  While I can see how they might have accomplished it, it's hard to imagine how that could possibly be safe.  It may even be photoshopped.  Pretty scary looking.
https://rvblogger.com/blog/how-to-level-travel-trailer-slope/

This is an interesting thread.  I too have a steep (asphalt) driveway (no idea what the angle is), but mine slopes toward my house.  There is a bit of a side extension of the driveway next to my garage, and that is where I am parking my T@B, it isn't as steep as the driveway, but it isn't nearly level and, like @kduck, I did have the trailer do a bit of a "scoot" once when I disconnected it from the hitch.  I usually use my Anderson levelers when I park it and chock both wheels, plus putting down the stabilizers, and, of course the tongue support -- figuring the more points of contact I have the better.  But I am still a bit nervous.  The last time I parked the T@B, I opted to forgo the Anderson levelers and leave the tires in full contact with the asphalt and just chocked them.  I really have no idea which is the safer way to go with this.

I have wondered about having some sort of curb installed at the end of the asphalt as an additional safety measure, but haven't checked into that yet.  I think I'll look into those heavy duty chocks, even the rubber ones I have seem rather small for the job.