Yep, you'll have to drop the generator to service the plugs. I know it sounds strange but it's true. The Marquis 7000 and 5000 both have housings that completely cover the generator. The only way to access the plugs, or most other things for that matter, is to drop the generator and remove the covers. It's not a huge problem to do but there are some things to take note of. You'll have to do the following:
1: Disconnect the negative battery cable.
2: Disconnect the fuel line. Remember to plug the MH side of the fuel line with a bolt after it's disconnected from the MH. It will leak fuel if not plugged.
3: Disconnect the battery cable from the starter solenoid.
4: Disconnect the electrical lines going to the MH. There should be a junction box near the generator.
5: Lift the MH on the left side with the leveling jacks to gain as much clearance as possible. It may still be necessary to lift it more and place it on jack stands depending on how you lower the generator.
6: Use either one motorcycle jack or two floor jacks to lower the generator. Jack them up to contact the bottom of the generator before unbolting it.
7: Remove the 6 screw bolts that secure the generator frame to the MH
8: Lower the generator slowly until it's resting on the jack/jacks.
Once removed you should be able to gain access to all the screws needed to remove the black panels.
OR, you could do the following.... Go to an RV center and have them service the generator.
As you can see it's a a lot for just servicing the spark plugs. Good time to service the rest of the generator. Carb should be cleaned and adjusted. Brushes and slip rings should be cleaned as well. These generators are notorious for frying the regulators if the slip rings get dirty because the generator has not been exercised regularly. Expensive part to replace and the generator needs to be removed to gain access.