Best I can tell looking at the history portion the "87 had a 60 gallon tank as did the "89, so you would expect the "88 to have the same.
The 17 and 18' animals in the "89 had a 52 gallon tank.
http://www.wellcraftv20.com/gallery/...og_v20steplift
http://www.wellcraftv20.com/gallery/.../017_wellcraft