A good practice when it comes to distributing propane
on a travel trailer is to run soft copper outside the trailer(underneath), and to make all connections that deliver propane
to an appliance, outside(underneath) the trailer. That way, all connections which can possibly leak , are visible and can be checked with soapy water or a combustible gas tester. If you only want propane
for your cooktop, I donít see a problem with running the line inside as long as you are sure the line wonít be damaged by stored supplies, tools, etc.. no inside splices or plugged t- fittings in hidden out of site locations.
To use copper lines you will need a flaring tool and to take some time practicing using it. I suspect there are some good utube videos that would be helpful.