Route 4 in New Hampshire and Vermont

With less than ten feet of height for your RV, just follow me and you’ll be fine.

US4 should not be any real problem. I don't know how particular you are about gas stations and what you can fit into (I've only found one or two that have given me any trouble in all my travels, but some seem to have quite different experiences), but there are at least a few that are very easy access along the way.

If you take the short section of I-89 where US 4 criss-crosses it a few times, through West Lebanon, you can get off in West Lebanon and get gas at Sandri next to the interstate. A bit south on 12A there's a BJ's with a (new) gas station that also has pretty reasonable access, though not quite as nice, and usually somewhat better prices even for non-members. BJ's is not open 24/7, though, unlike the Sandri one.

Near the NY border, there are a couple of good truck stop/gas stations on VT 22A right by (just south of) the interchange with US4 that have wide open access. I'm pretty sure there are other nice open gas stations along the way, but those are the ones I can think of offhand.

Your wife must be into quilting. When we take our motorhome from Maine or NH to Lake George we usually take 89 out of Concord up to just past the CT river and take the road through Woodstock, Killington and Rutland, then to Whitehall and down. That is not as scenic as your road but we're 45' and towing.

We have driven your route many times to see relatives in Ludlow. It's a very pretty ride and you shouldn't have issues with a 26' trailer.