I am an older lady who drives a 32' Class C, and have put 95,000 miles on it in five years of full-timing. I have never towed anything, and have managed to get into almost everywhere. Mostly, I shop at grocery chains that have large parking lots, and places like Lowes. Larger shopping centers are also easy. Generally, I park at the far ends of the parking lots where there aren't any cars. Then I can take up two spots end to end. Sometimes I park lengthwise and take up 5-6 spots, but only when there is lots of room. I try to find fast food places that are next to shopping centers, etc.
Almost all museums and attractions will have space for big rigs. I always call ahead if I am concerned and take their advice on where to park.
And I have almost never found a campground too small for me to park in. Almost all state and national parks can easily fit in a 35' vehicle. Look around at campgrounds using Reserve America and Recreation.gov to see this. You should have absolutely no problems with 25' unless you want to drive through downtown San Francisco, Boston, and similar.
This came up recently and had several good answers. Here is the link: http://www.rvforum.net/SMF_forum/index.php/topic,102874.0.html
When you first start out, a motorhome will seem HUGE, but after a few days on the road, you will get much more comfortable. After all my travels, by the way, driving a car feels really weird. Now, I will wait for Miss Mermaid to chime in, as she drives a 28' Class C without a toad, and has done so for longer than I have. Both of us have electric bikes for tooling around campgrounds, however!
