It looks like you're new here. If you want to get involved, click one of these buttons!
I'm in the process of adding insulation to the underbelly and will be covering these holes. I'm going to put a small vent at the rear and one at the front to let any propane gas escape. While there are no propane devices in the underbelly, there are several pipe connections. If one ever started to leak, I wouldn't want the gas to accumulate in an enclosed area.
Cliffhanger - GregH is the first one to add Alde mini-convectors in the "basement." I just connected the lines with 4 mini-convectors and a PEX line to the dump drains. Will fill the system today and check for leaks. Photos coming coming this weekend if it works out.