Largest RV show I've been to was my first, Florida RV Supershow in 2004. Even that was the same, regional dealers, but with some extra units brought in for the show. My biggest problem with the large show was that many dealers put on extra sales staff for the show, and most of these extras know nothing about RVS.
On the other hand, even at smaller shows (I've been to at least 30 over the past 12 years) many of the manufacturers send representatives, the people from their sales staff who sell to dealers, and these usually know what's going on, but they don't always know what is in inventory back at the dealership.
What is going to be at the show will be what the dealer carries, some representative fraction of the inventory, and that will be mostly what sells well in the region. Tulsa show (at least two a year) this means mostly entry level and/or ultralight travel trailers, large toyhauling fivers, a few Class C and entry-price Class A motorhomes, and a handful of luxury Class A motorhomes in the $200,000 to $400,000 range.
At Oklahoma shows, very seldom do we see truck campers (they just don't sell well in this part of the country) or pop-ups (most dealers have quit carrying them since the price got close to the cheapest TTs). I see truck campers (a few) and a lot of pop-ups when I go to shows in Michigan and Indiana, that's a different market for a different camping environment, different camping tastes.
I don't think there is any show where manufacturers show up with one of everything, especially since there are some models for which few will be built, because they build only what dealers will order. Maybe the largest shows (Hershey, Quartzite, Los Angeles) will be different, but I don't think so. Most states require a dealer license for sales at a show, so even with factory participation you will still be visiting dealer displays.
Tom Test
Itasca Spirit 29B