Welcome to the forum.
I wouldn't consider a trailer with cable operated slides. I would also make sure the unit you are considering has tire and axle ratings that aren't maxed out at the weight you will be towing. I like safety margins and a unit with a high cargo carrying capacity would ensure that.
If it has a membrane roof it will have seams and will be susceptible to leaks and will require periodic maintenance. Trailers with solid roofs and no seams (fiberglass and aluminum) generally don't have slides.
Good luck and consider shopping as part of the fun.