To add DC you need the eyebrow board and everything that connects to it. There is no kit. It is not a simple add-on.
Whether propane poses a danger while underway has been debated across the Internet for decades. I would simply suggest that if there was a significant risk it would also be a risk to the manufacturers who made it possible to run down the road with the propane on.
My underlying thought is propane poses no more risk while traveling than while camped, unless the argument is that you might catch it sooner while camped and I guess that is true provided you are at your camper when the fire starts.
I agree with Mike. If operating on battery power is an important goal, change out the entire fridge and go with a DC compressor model plus the solar to support the batteries while it is cooling.
My two cents
Steve and Andra
2012 F350 6.2 gasser SRW LB
Fab Fours front and rear in case we run into a rhino
2019 Northstar Laredo SC