We have a 30 gallon "original" style Barker tote which is the two wheel style. As far as capacity, it is big enough for us. The downside to the two wheel style is it has to be lifted to the hitch ball for transport. Although it's not an overwhelming lift, it is a handfull. Also, the location of the spout on our tote is not ideal. It should be on the very edge of the tote but it's roughly 3 inches or so from the edge. As a result, it is difficult to completely empty. My recommendation woud be the new 4 wheeler style. Looks like it's much easier to handle when full (no lifting) and the spout is located on the bottom which should allow it to drain completely.
Kevin & Janine
2006 Dodge 2500 Megacab CTD 2WD
2012 Palomino Sabre 32RCTS
Pullrite Superglide 16K Hitch