Fuse (30 amp) keeps blowing at the inline battery 2017 outback

I've had my new Tab outback for two weeks . I took it camping 4 days last week. When I got it home I went inside to and found that nothing would power up.....everything was dead which surprised me because I thought the battery would charge up on the 2.5 hour drive back home and all the running lights and turn signals on the trailer worked fine as I drove home. . So I hooked up the shore power but everything was still dead. I looked at the breakers and fuses under the drivers bench seat and noticed the 15 amp breaker was flipped off. I flipped it back on ..still no power to the tab. I pulled out the 30 amp fuse on the converter box and lo and behold everything came on. Went to the tongue and opened the propane and battery box and checked the in line battery fuse.... it was blown. No problem. Went to radio shack and got 2 fuses got back home and put one in...it blew immediately. Put the 2nd on in . It blew immediately. Any thoughts as to what I'm doing wrong or what could be wrong with the outback? Thanks.