Roof air not draining and leaking inside coleman unit

Ur drainage tube is plugged so look for it and unplug it or change it it's called condensation tube

Water in an air conditioner is generally condensation building up on the indoor coil. This happens when the temperature of the coil is below the current dew point of the atmosphere. You have possibly two issues going on.

1) the condensation drip line, which carries the water to the outside is blocked or disconnected (most likely blocked with wet dust build up etc) and can typically be cleared by using an air hose to blow the blockage clear.

2) excessive water can be an indicator that you may have a slow leak in the refrigerant system. reduced pressures will lower the temperature of the coil causing it to condense more water, more frequently. While you might enjoy the seeming better performance of the unit, if there is a leak it will eventually reach a point where the water will freeze(cutting off the air flow so no cooling) and eventually stop working altogether. Have a certified technician check your system for leaks. Remember that most rooftop units use R-22 refrigerant, not R-134a automotive refrigerant. The wrong refrigerant in the system can be very damaging to components and seals, and can cause the unit to function improperly.

have to remove cover to access drain lines to clear

If it's leaking inside where filter cover is, then real good chance the drains being plugged is the only problem. If water (condensation) not running off roof when operating in cool mode, then I'd bet drains, which are located under unit on roof, and you should see them sticking down like buttons. They have a hole in side that needs cleaning with a pipe cleaner or similar to open them up. If need be, shut off power to unit and remove top cover on roof unit and look for the drain holes in base, and clean them out. If water comes in while raining, but AC not running, then it's gasket. That is remedied by removing ceiling assembly (just screws) and 4 bolts that pull/hold the upper and lower assemblies together, unplug wiring to upper unit, and simply lift it off, change gasket and re-install. Tighten those 4 bolts equally when gasket is aligned properly over hole, only until gasket is approx 1/2, original thickness. Plug harness back in and your done. (about an hours work.) Only other thing that may be wrong is styrofoam drip tray for cooling unit, under cover on roof may have a crack , allowing condensation to leak in. If that 's the case, you can try to find a sealant compatible with styrofoam to seal those cracks.

I've not run into the problem your having yet, so I will apologize up front for asking you to furnish more information. These drain cups that I assume are little round pieces attached to the base of the unit where it meets the roof, were not common on dometic, but were common on Coleman AC units. Those are the outlets for condensation to the roof anyway, are they not?
Also, as far as gasket goes, no I wouldn't recommend using 2. We were always advised by manufacturer to compress gasket to half the original thickness when installing either Dometic, or Coleman (RV Products). Coleman at one time, had tabs under gasket that when gasket was compressed, and they touched the roof surface inside, that was far enough, which was approximately half the original thickness. Believe it or not, over-tightening is more likely to cause a leak. Stick with half original thickness, or close to it.

Check on roof, look under at base of AC unit for 2 knob like things sticking down, they are drains. use a piece of wire or small stick & try to poke inside there. You might have to look hard to find hole. Pay attention to run off on roof, if not as much as usual, that's a good indication they are plugging up. If too hard to get to, remove 4 screws & pop cover off, but watch for wasps or yellow jackets before you do.

Check for plugged drains under cover on roof, sticking out at base of unit usually. It should be running off roof.

Check run-of on roof & see if it's been reduced lately, it may just be a plugged drain at base of unit on roof.

Does water drip out of unit on the roof while running ? If you look under the unit on the roof, you should see one or two little drains sticking down., that may be plugged up. Piece of wire or something and poke in the holes on the sides of those drains to make sure they're clear. Usually there is a plastic/nylon pan on roof unit to catch that moisture, and drain it off. Could be overflow because of the plugged drains, or I have seen the odd one crack but not too much recently, mostly back 5 yrs ago or so they had a run of them.

Under the drain pan on each side should be a small plastic drain plug they might be clogged up with debris.