I think you've been frightened by people talking big $ for mobile service ..incorrectly ! The tow alone is a big expense Your in a parking lot safe . This problem is a big truck problem not as much a Rv shop repair problem ... The last place I'd look btw . There are thousands of truck repair and mobile truck repair places all across the country and many work on Sunday As a commercial driver I've gotten service on Sunday on my tractor or at least my company has .. Time is money
A proper truck service shop can probably have you on the road quickly perhaps a motel until Monday would be cheap and a better solution , if you don't feel safe , until a qualified mechanic can look at it
Tow only when you can't fix on the spot
Btw the tow can energize the air system by the method you are thinking about air line to fitting but if your compressor is working then that may not work and if not they will back off the spring brakes ... With a wrench on the air can. Let someone who knows how do it .
