Your roof vents are RV industry standard. If the leaks are in the plastic cover, replacements are available at any RV dealer and there are lot's of online sources.
The small round vents, if they are just a few inches in diameter are probably the covers for the vent stacks for the plumbing system. Standard stuff, available at any RV place or online. Gentle heat to loosen the caulk.
If the leak is around the perimeter of the frame of the vent where it is fastened to the roof, then your fix is more of a roof repair than a vent repair. Depending on the size and extent of the leak, you can caulk well before sealing the roof.
Sealing the metal roof comes up regularly. There are a bunch of detailed posts in Repairs and Maintenance about that. The short answer is repair and caulk, then seal the whole roof with a coat of mobile home roof paint, available at any hardware store, paint store or home improvement center. When I had metal roofed trailers, I bought a throw-away brush for this. On a 19 foot trailer, I did the seams twice and then the whole roof. There was a little bit left over of the gallon that I bought.
Almost every installed item in your Sunline is industry standard. The only things that aren't are the stuff that Sunline actually fabricated like cushions, cabinetry, etc. Even there, the hardware is standard stuff.
'12 F250 4x4 Super Duty PowerStroke 6.7 diesel
2011 to present: '11 Cougar 326MKS
1999 to 2011: '99 Sunline T-2453
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