DSI is well worth the money, especially if you have to go outside just before a shower to ignite a pilot. Plus, you will not be wasting propane while he pilot is lit.
If you want the best (IMHO)water heater, look at the Precision Temp RV-500. It has no tank to keep hot and heats the water instantly. It will give you as much hot water as you want, limited only by the amount of propane available.
I replaced the 6 gal. that came with my 19CCD and had to do a little 'surgery' to the skins as well. It is not a problem if you are careful and precise in your measuring.
Solar Tech Energy Systems, Inc.
Victron Solar Components and Inverters, Zamp Solar Panels, LiFeBlue and Battle Born Lithium Batteries, Lifeline AGM Batteries