Can it be done? Sure.
Just don’t forget a ‘homemade’ camper or tiny house with plumbing, electric and propane systems won’t be legal anywhere but your own property and likely not even there.
I’ve built several over the years, mostly as deer camps on wheels kind of setups. The above folks are right, it’s VERY easy to get it waaaay overweight.
If you look up the videos on YouTube or such of the construction of a travel trailer you’ll see why they deteriorate or blow apart in a minor accident. Most of the ‘structures’ is 2” x 2” pine, the panelling and siding are structural elements.