Maplenut,,, welcome to the RTV Forum.
Regarding your question about the weight you cab "comfortably" put in the bed. The operators manual for a 2012 1100 RTV states a weight of 1,100 pounds. Now as Paul Harvey used to say on his radio show, ,,," and now the rest of the story." I don't know what the weight of your 225 gal tank filled with sap might weigh. Besides that weight, several other factors to seriously consider. That sap sloshing around as you travel might create a bad situation. Hills and slopes to consider. Higher center of gravity might create a real "pucker factor" with a full load. Hate to see ya lose a load of sap and a new RTV in one fell swoop. The RTV 1100 has a higher center of gravity because of the cab. Just throwing some items out there for you to consider. Have you thought of using a lower to the ground bed on a tow- behind= trailer? With a 1100, the manual says you can tow a rolling weight up to 1,300 pounds. Just some food for thought.
Good luck with your purchase.