I'd go with some vinyl floor covering and if the floor boards are in good shape, just use the same kind of adhesive as you would in your house. Then I'd put down some rug runners where you want them.
In my trailer, it has carpet laid around the front queen bed and the rest is vinyl. I have rugs running up the isle and the entrance and that helps a lot. The carpet around the bed is cheap and not much padding.
But if wall to wall is your plan, I think it's just laid the same way they do it in homes. My dad had his RV re carpeted and it turned out pretty nice. He had thicker padding installed and it's very 'cushy'. He left the kitchen and dining area the stock hard wood flooring it came with. He used home grade "berber" carpeting..
Good luck!
Mitch
2013 F150 XLT 4x4 SuperCab Max Tow Egoboost 3.73 gears #7700 GVWR #1920 payload. 2019 Rockwood Mini Lite 2511S.