Spent three months campground hosting at Big Bend last summer and two months at Davis Mountain SP last fall.
The only part of TX-118 which isn't favorable for RVs is the section above Davis Mountains SP toward McDonald Observatory and on to the I-10 junction at Kent.
Even that is okay if you take it slow. TX-118 from Alpine to Study Butte - smooth, WIDEEEEE, easy route. A few hills.
Don't know where SR-365 is.
US-385 from Fort Stockton to BBNP is also a very wide, easy route. Great shape for highway. If I was going from Fort Stockton to Alpine - I'd take US-67 rather than US-385 to Marathon and US-90 to Alpine. (But we use US-90 from Del Rio to Alpine vice I-10 - much better drive.)
TX-17 from Balmorhea to Fort Davis is a good road, a little twisty through the pass, but nothing difficult.
The biggest 'issue' about taking US-385 into Big Bend NP's north entrance is the 45 mph speed limit in the park. It's about an hour and a half from the north entrance to the west entrance.