By trailers, I assume you mean mobile homes, correct?
If so, I think it primarily depends on your location & the demand for them in your area. MH's are something I've been looking into, as well, because as you stated, they are cheaper to purchase, renovation costs are *typically* cheaper, and the demand is still possible. For example, I know certain places in my area where MH's are allowed/not-allowed, so this helps to cut down on that guesswork. I also know there is a demand for MH's within & around my area, and the rent is decent in most places- put decent rent with low purchase prices and it seems to be a wise investment. To me, MH's seem to be an easier way to get into REI without having to pay thousands of dollars on a home- instead, those extra thousands saved could be put towards saving for another rental property, repairs on your current rental properties, etc.
Just make sure to research your area, figure out the demand, make sure purchasing a MH is more beneficial & more sensible for you than buying (or saving for) a larger investment. Keep in mind repair costs, surrounding land conditions, and wherever the mobile home is located, make sure they allow manufactured homes, or if in a MH park, make sure they allow rentals.
Good luck!