Sorry, I haven't converted one of these. This might not be the best forum to ask for advice on subs such as your building, most of the people I know who have converted these dont frequent this forum any more. Look at one of the more sub specific sites. Of the 3 commercially avilable WTC, the gas one is the easiest to get get going but has the most chopping up of the main hull, the water pump is the neatest install and should be the most controlable with a peristaltic pump, though again you need to chop the hull. The RCABS is the most complicated and toughest build and performance should be somewhere between the other 2.