Well, you came to the right place for this question. ;D
There has been some concern with the basement air in the Winnebago class A's being large enough to handle the load of units that are longer than 35 feet with several slides. For 2009, Winnebago has upped the capacity of the basement air for any unit that is longer than 35 feet.
Yours and mine fall into this "size" category with our basement air. :'(
There are several problems I see with the cooling system as currently used by Winnebago.
1. Lack of insulation in the "box" structure by Winnebago. Where the roof is attached to the sidewalls are not insulated and the extruded aluminum joints the run the full length of the motorhome sides are not insulated. Above the entertainment center along the front cap receives a small "blown on" foam coating which is very low R-value.
2. In some 2004/2005 models, there have been some cases of separation of the rear "Y" rigid ducting that comes from the basement air, then "Y"s to both ceiling ducts UNDER the rear cap. The way to check this is to get under your motorhome and reach up as far as you can and feel along the rigid duct that goes to the "Y" and see if you have cold air escaping. Another way is to use a hand held pistol IR thermometer and see if you have much temperature change when you aim it at the "Y" area of the ductwork. I have done both with mine, and I can't see anywhere where the cold air is escaping. The only other way is to remove one of your tail lights and run your hand toward the duct to see if you feel cold air escaping/and use the IR Thermometer gun around that area. Other owners have said that if you run your hand over the rear cap and feel cool temps where your rigid ductwork is, that you might have a leak....I didn't find that the case even though during hot days, I can run my hand on the outside of the rear cap where my duct runs, and it is noticiably cooler than the rest of the cap.
What we have done about this, and what you can do:
1. Cover up the OUTSIDE of your very large BTU loss Windshield with a Sunscreen. Many of us have used these with VERY good results. I use
THIS type on my windshield and front side windows to block the very hot sun. Also use and install Window Awnings....I did which is an EXCELLENT way to keep the hot aluminum window frames COOL. The key thing is to get into as MUCH SHADE as you possibly can so the sun can't make that glass and fiberglass sidewalls so hot! Use your main awning if your curb sidewalls is in the sun....you would be amazed of the temperature differenct as you remove the sun from these sidewalls!
2. Open up ALL your flow vents in your motorhome for good air flow....even the ones in the bathroom.
3. Keep your inside filter clean. I just got off the phone with RVProducts (manufacturer of the basement air), and they recommend the cheap blue fiberglass filters. He told me that if you can't "see your hand" through the filter, don't use that particular filter.
4. Start your cooling process EARLY in the morning...it's ALOT easier to keep a cool motorhome cool, than a hot motorhome cool. Trying to cool off all the interior hot couches, tables, chairs takes a long time.
5. We have pulled in our kitchen slide (we have opposing living and kitchen slides) during the hottest part of the day, and that helped the cooling as the slideouts are not insulated very well.
I have owned several other brands of motorhomes, all having roof airs, and they all could keep down the temperature inside. My current Winnie with the basement air will keep the inside temps similar to yours with similar outside temps, so we do the above steps to help it as best we can.