Heating in the oven really doesn't work unless you've opened up the unit completely. The moisture in it just gets warm, evaporates inside the unit, and then condenses later, possibly in areas where you can't see it. It's actually better to just move a lot of air through it. You can use an air compressor if it has a moisture trap, or a small fan aimed into it. Or dry air like nitrogen if you have a source. You can also use a vacuum cleaner against one of the vents or bulb holes, forcing air to be sucked into the others. This works best on a low setting or with a small cleaner like a dustbuster that doesn't generate too much vacuum, so it won't overheat itself. I have one of those small clip-on fans at home that works fine for stuff like this, and I've used a house vacuum on very low settings more than once. Any of these options usually work better and faster than an oven.
Also if you really want to use your oven, I recommend you not let it cool off in the oven. If you have a gas oven, that's moist air - when gas burns it creates water and CO2, meaning even more moisture in the oven. All that will do is heat up what air is in the unit, causing it to expand and some of it will come out of the vents, and as it cools it will suck the moist air back into it. Even if it's electric, some of that water that evaporated out will get sucked back into it as it cools.
And be sure to put at least one heat shield if not 2 between the oven heat source and the unit. If it's gas, the vents that let the hot air up from around the burners are letting in much hotter air than what the oven's average temp will be. If it's electric, direct heat radiation from the elements can be up to 450-500 degrees.