Here's another 150AH AGM deep cycle model you might want to price. It's the model I'll look seriously at fitting a couple of into our RV's existing batttery space if I ever want to replace my fairly new 115 AH Group 31 AGM deep cycles batteries - it's a couple of inches taller than my current battery model, but it's other dimensions are similar. The reason I picked these over Lifeline is their recommended float voltage spec. The Lifeline specified float voltage is lower than what my converter will float them at hour after hour, on average:
http://www.fullriverbattery.com/product/batteries/DC150-12