I have had the same problem many times, with Urac, but even more with TBII, since it doesn't fill the gaps as well. Also, I think the water base made some wood lams want to warp or cup as the glue dried at the same time water was soaking into the wood to some degree.
I started out using innertube clamps, but I like experimenting and change my forms all the time, etc..and got a bunch of those little spring clamps so I didn't have to put dowel pegs into my forms, etc.. They did not work well. Just didn't...
I broke down and bought 30 small c-clamps and, with a few innertubes here and there, am getting by better and my glue lines are prettier...