Towable RVs tend to look and feel "flimsy" because they are lightly constructed to enable moving them around constantly with light-duty tow vehicles, and to reach price points that makes them accessible to buyers. There are better-built RVs, at much higher prices, and they have quite low sales volumes. Even with the better RVs, there are compromises for weight control and mobile use, compared to manufactured housing. They also have to be self contained, so that you can park anywhere and live in them.
Tiny houses, even when built on wheels, are more often built using permanent housing construction methods and materials, and thus might be several times heavier for the same floor space (and are usually lofted for additional living space. These are meant to be moved to a semi-permanent or permanent location by more capable tow vehicles. What utilities they have, relationship to infrastructure, varies a lot with the owner-builder intentions, some are just little houses fully on the grid, and at the other end of the scale they can be totally off-grid and back to 17th century lifestyle, or anything in between.
Manufactured housing, descendant from the house trailer and mobile home, is built to HUD standards for permanent occupancy. This makes them much heavier than RVs (especially considering the HUD standard includes a minimum size) and more standardized than tiny houses with respect to facilities and performance. They are meant to be put on location by a fairly large tow vehicle (or team of tow vehicles for double-wides) and hooked up to power, water and sewer like a stick-built house.
Park model RV is kind of a odd duck. Most are at maximum size for a RV, some cross over into manufactured housing sizes by stretching the meaning of the HUD rules. They are usually heavier than a "normal" RV of similar size and often require specialty towing. You will find a spectrum of features ranging from RV facilities for long term hookup at a RV park to mobile home facilities for permanent hookup in a mobile home community. They are almost always built to RV construction standards, intended for part-time use, or short term use, but they can do pretty well in less stressful climate conditions.
Park models, instead of mobile homes, are often used for temporary housing at remote work locations because they are light enough to be moved to the next job site after a few months or a few years. You can run into trouble with housing code enforcement if you try to use park models or even smaller RVs as permanent homes. It can also be difficult dealing with power companies and water districts, and the folks that have to enforce sewage disposal standards, if you try siting a RV as a house.
But tiny home folks have to deal with these same issues, or sometimes even putting a mobile home on a remote site. So it can be important for planning, and choosing, that you learn about the regulatory situation at your place of interest.
If you are not moving around, you are not really full time RVing, but this is probably the best place to ask your questions.
