Les,
When I bought my coach almost all of the gas shocks, or hydraulic lifts, were bad. I ordered mine from SPD Hardware at
http://www.spdhardware.com/ These are the same brand that came on my coach. I have used this company for about ten years & they have always been helpful & shipped quickly. Each gas shock on my coach has a tag that identifies the shock & its pressure or force. The gas shocks that you need are the "GSNI Black Nitride Shaft Gas Spring". Using a shock with too much pressure or force can cause your mounting points to fail. These are items that will commonly need replacement with use. If your shocks do not have readable tags, private message or email me your tele # & I'll call you and give you the proper pressure for each bay as they do vary.
When you replace them you will need to compress them about an inch. I was able to compress the ones where I could access both mounting points with a pipe clamp. I have since copied a tool that Newell made to change them. I attached a photo of the tool. Using the tool you attach the rear gas shock mounting point, put the tool over the door hinge crossmember, place the unmounted end of the gas shock in the tool's rounded slot, compress with handle & slip onto shock mount. Pretty simple with the tool. This tool works for the bay doors, but won't work on the engine cover shocks. Russ White's idea of using a hydraulic jack seems like the way to go when I have to replace them. TIP: When working on side with the mercury tilt switch for the bay light unscrew it & move it out of the way as it can get broken.
Hope this helps..................