I have a 2000 Sundowner Valuelite and it also leaked a couple of years ago. My problem was the seal on the roof where the radius corner pieces meets the aluminum sheet metal that covers the roof. What I did was to clean the whole seam with warm soapy water and coat it with an elasto-matic coating made for mobile home roofs. I only did the seam not the whole roof. I would put a coating on the seam and let it dry before putting on another coat. I did about 6 coats to seal it up good. Now this might not be the best way to fix the problem or might not be the right stuff to use but it has worked well for my trailer.

 You may need to put a bead of clear silicon around the trim at the bottom edge of your horse trailer nose if you think the water is coming in there. But water is tricky to determine where it is coming from so I would look at all areas and seal anything that looks suspect to leaks.

I have a valuelite too. The windows were leaking at the seal.  I pulled the windows and replaced the gasket with EPDM closed cell foam tape. Then recaulked between the side and window fram for appearance. (the window is held in by the torx screws through the interior frame )

The roof seam between the roof sheet and 1/4 round also leaked.  I fixed it by recaulking it with the OEM sealant.  It's a sikaflex product.

Would I need to worry about leaving a sticky residue behind on my painted aluminum trailer walls?

Also, in lieu of soapy water, my husband tells me that where he works they use a product called Snoop.  Not sure why he's suddenly becoming helpful now, when he knows I've been trying to find this leak for the last two summers already.  Oh, the frustration!  I'm definitely going to try this fan idea.

I cut my plywood a little larger than the opening of the door, drilled a hole in the wood large enough to put the top of a "C" Clamp thru. And clamped the wood top and bottom. I had a little leakage around the door but the fan put enough air into the trailer that it worked just fine. It dosen't take much pressure to get it to work. If you like you could put the foam on to the plywood for a better seal if your fan is weak.  Soap is cheap and it works just fine, I put about 1/2 a cup and water in a one gallon srayer and it covered the whole trailer. It isn't my idea, someone told me how to do it. Maybe the converters will read this and pre check their trailers before they ship them.