Bski, when you are planning to clear span the entire 28', remember that when they are being designed to code (L/360 or higher, hopefully) that you could have up to an inch of deflection in the entire span, and still meet code. You may want to reconsider such a long span, so that you have a stiffer floor.

-Chris
1 acre pond
Currently managing:
FHM, GSH, GSF, BG, PS, RES, LES, YP, SMB, LMB, HSB, RBT, WE, CC, FHC, and Grass Shrimp