What is the max length travel trailer you think is practical

25' with a slideout is probably the max I would go for hitting State Parks (in WA) and some national parks.

A lot of the national park campgrounds were built decades ago, when the typical tow rig was a family sedan or station wagon, with a 15-20' trailer.

I really like the Arctic Fox 25R or the Nash 24M.

Both have a slide, sofa and dinette, and a walk-about bed