OK. Got them installed this morning. Took about 4 hours but there was a lot of head scratching and problem solving (thinking) time involved.
First I lowered the wood panel for better access to the top vent behind frig on back of slide out.
Then removed old fan and thermistor.
Checked connections with voltmeter and found that fuse was burnt just at the positive terminal in lower vent. Direct connection showed fan does work so decided to use it still in a new location.
Next, screwed a small lightweight board approx 3/4" X 1.5" and 15" long to the holes where the original fan was fixed. Used this as a mounting base for all three fans.
Mounted original fan in center with original hookup including thermistor.
Direct wired two new fans to pos & neg with a switch in lower area. I can turn these on as needed on HOT days or when no shade available.
Picture showing difference in size - new and old fans.
Here's where the head scratching started. All three fans blow downward. I tried wiring them backwards and they will not run at all. Only +to+ and -to-. They are mounted upright. If I turn them over, the bearing area is exposed to weather more. There is a shroud type cover in the center of each fan that seems to indicate up and down. Why won't they run backwards when wired backwards? At this time, a huge storm blew in with nearby lightening, and I dismounted my ladder olympic style. Will think more on this issue as oright now, all three fans are blowing downward and that is not what I want. Hope someone has some advice.
Here's a close up of the board mounted.