will any stackable washer/dryer combo fit in 5th wheel space for washer dryer

Depends on both the space available in the 5th wheel.. and the size of the stackable. 

Measurements are needed. There are different sized stacked units, and your space will dictate what is available for you. I have a combo unit, but I think I can expand my cabinet for a stacked if I want. I would prefer not to add the extra weight, and the combo unit works well for me (solo). I dig having a washer/dryer!