Are you SURE nothing is on in the trailer? My 2007 HiLo was bought new and it had a radio/TV/CB/DVD unit installed that was NOT "switched". It was connected directly to the battery, bypassing the Master Switch. The battery ran down in it too, due to the "keep alive" circuitry in the radio. When I finally figured this out, I installed a simple on/off switch in it's power line, which stopped the power drain.
I think the 15W solar panel that HiLo offered as an option, is mostly a decoration. It supplies very little power.
If your battery did not charge when you were driving it around, your vehicle's 30A fuse to the battery charging wire may have blown. This happens very frequently when you raise the top of the trailer with it connected to the tow vehicle and the TV's engine is running. If the trailer battery is weak, the lifting motor will pull enough Amperage through the charging wire to blow that fuse. I always disconnect the trailer before operating the lift system.
If you put the Master Switch in the middle position, it SHOULD turn everything in the trailer off except for the refrigerator.
Hi-Lo 1707T - Tire Minder TPMS on Tow Vehicle and Trailer, 300W Solar Battery Charger, Equal-i-zer WDH
2014 F150 Platinum 4x4 3.5L EcoBoost SCrew