It is not the wheelbase you look at by itself - otherwise, everyone would be buying 45' rigs; they have the longest wheelbase. You must consider it combined with total length of the rig. The wheelbase will be a percentage of the total length; the general recommendation is to look for a ratio higher than 50%.
However, I will also suggest looking at chassis gross weight rating. At the size you are looking at, it can range from 14,500 to 22,000 lbs. The higher the GVWR, the 'heavier duty' the chassis and the more it can carry and tow. In our search, we saw class As with a cargo capacity as low as 1200 lbs and tow ratings as low as 3000 lbs. Can't carry or tow much of anything with those.
With 4 dogs, I would suggest the higher end of your length range. Best of luck in your search!
2015 Jeep Willys Wrangler
2014 Fleetwood Bounder 33C
States camped: all but Hawaii
more than 1700 days on the road