Any opening or seam in your trailer's roof can be a water leak source. It doesn't have to be completely on the top, a marker light, vertical seam, window caulking can all be a culprit. A LQ trailer has a greater chance of leaking than one with just a dressing room. All the vents, air conditioners, antennas add up to a lot of caulking to seal the lot. Water can travel a significant distance. Where the water is found, may not be in the same area as the actual leak.

Caulking has a limited life span, dictated by your weather's environment, type of storage, the quality of the installed product, and the skills used during its installation. Five to eight years is not an uncommon life span in poor conditions, a decade is stretching the limits of a leak proof roof. 

The old caulking has to be removed before any new is applied. Marine quality polyurethanes are far superior to the common household silicone variants. Elastomeric products are also proving to be a good sealant.

The smallest crack in the caulking can be a source, remove the running lights and look at the sealant under their bases. Every seam should have a new flexible seal, that can move under the expansion and contraction of the various materials. The old caulking gets rigid with age, and cannot maintain its flexibility, which causes it to fail and pull away from the surfaces.

If a visual inspection can't resolve the issue, the best way to find a chronic leaks is to pressurise the LQ's interior, and apply soapy water to the various exterior surfaces. Any resulting bubbles will indicate exactly where your leaks are.

An old squirrel cage fan from a furnace is an ideal source of air. 2nd best is a common box (20") fan available almost everywhere. Measure the area of a sliding window in your DR or LQ and cut a piece of plywood to that size. Cut a hole in the middle of the wood the same size as the fan's outlet. Screw the fan's frame to the plywood. Drill a hole near the top of each corner and thread in lines, long enough to go over the top and across the trailer to a point, where each can be tied to something that will support the fan's weight.

Grab a roll of duct tape, and seal the edges of the plywood to the window. Make sure all the other windows and vents are closed, tape them if necessary. Turn on the fan, wait a couple of minutes, and then apply water mixed with liquid dish washing soap to specific areas of the roof. If any bubbles appear, wipe the area and reapply the soap/water combination until the exact source of air is determined.

A box fan will not apply as much pressure, but it will work if you look carefully. Again the sides of the fan will have to be sealed around the opened window. If any obvious air leakage is noted from other windows or vents, they should be taped so that most of the air is escaping through the leaking roof point(s).