If you are flexible in your choice of towbars, your might be able to solve your dilemma by using a Blue Ox tow bar. If you have a heavy duty after-market front bumper (stockers are pretty flimsy) you could use Blue Ox's Bolt-on-Tabs. I have an ARB front bumper and I bolted the tabs directly to the front surface of the bumper. The tabs come with a steel plate to use on the back side of the bumper to beef it up, and I have read on other threads about people who have successfully done this with a stock Wrangler bumper with no complaints. Personally,I feel safer with a more substantial bumper. I couldn't fit a baseplate on my '06 Wrangler because of the lower bumper design and my winch being in the way. The tabs are Blue Ox part #BX1108 and only cost $68 for the pair. They should be installed approximately 24" center to center, and are supposed to be as low as possible on your bumper. If you are lucky, the Roadmaster tow bar will fit the Blue Ox tabs, but I'm a real believer in the Blue Ox products. The Aventa II is a great tow bar.
Good Luck, Rick Coleman
'05 Alpine 36MDDS