As far as following the salesman's recommendation on buying a 45' motorhome goes, IMO you should buy the size and style motorhome that suits YOU and not try to predict what may or may not hold its value at some unknown time in the future.
The salesman's recommendation may be based on trends he is seeing now. On a recent visit to the Tiffin plant in Red Bay, AL, we saw their production is down at least 50%. However, most of the motorhomes we saw on the assembly line were big Allegro Buses and Zephyrs. These are Tiffin's 2 most expensive motorhomes costing about $300k+ and $400k+, respectively. I suspect those with enough money to afford these coaches don't really care if diesel fuel costs an extra $2 a gallon or not, so sales of these type motorhomes are not off as much as the smaller ones. That seems to be the current trend, but with rapidly-changing oil prices and the current economic situation, who knows if this will still be the trend next year or the year after that. No one can predict. That's why I say buy what suits YOU.
As others have said, campgrounds run the range from primative to luxurious. You can camp in wide open spaces with no hookups like BLM lands in the west; in small, crowded campgrounds with lots of older trailers and semi-permanent residents; in luxurious RV resorts; in quiet state parks; in beautiful locations like national parks; and in all types of campgrounds in between.
You are correct in trying to find out what kind of campgrounds are out there. This is a good first step. IMO, you need to determine what kind of camping you want to do before deciding on what type and size RV you want. Do you even want a motorhome or would a 5th wheel suit your needs better? If you're new to RVing, I suggest visiting as many RV dealers as you can and at least one larger RV show.
Ask yourself some questions like do I like to be in a natural setting or a controlled, landscaped setting? Do I like shade or sun? Do I like peace and quiet or lots of people and activities? Will I stay in one place for several weeks or months at a time or will I move to a new location every few days? Answers to these questions will help determine what type and size RV will suit your needs.
I also suggest looking at several campgrounds in your area to see what amenities they have, how close the sites are, how crowded they are, whether or not they have shade, etc. Check out an RV resort; a small, private campground; a larger, chain campground (like KOA); a state park or a Corps of Engineers campground; or whatever might be within driving range of where you live. Most campgrounds are happy to let you drive through to take a look around. You won't really know what it's like until you stay in a few, but just driving through may give you a good idea of where you want to start.
Get on the internet and search for campgrounds in areas you think you might like to visit someday. Many campgrounds have web sites showing pictures (caution: the pictures frequently make the campground look better than it really is), rates, amenities, activities, etc.
This is a big decision to make in these difficult economic times. Best wishes.
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