An iguana's perfect climate is very warm, damp, stuffy, and odorous to humans. Humid air holds more scents. A human's perfect climate is cold and very dry to iguanas.
I suppose the condensation is running down the front, wetting the substrate. This will cause mold which can make your ig sick and is very hard to eradicate.
Plexiglass is a lot more insulating than glass, which would get even more condensation on it. This is a typical problem with the levels of humidity that iguanas need. I believe the plywood (3/4 inch thick, right?) parts have enough inherent insulation to avoid condensation at 75% humidity. But to be sure, you can add 1 inch foam insulation to the outside plywood surfaces. If you want to, you can glue 1/8 inch plywood over the foam. Some glues dissolve some foams, so pick the right glue. latex caulk would work (clear latex caulk if you can find it is non-toxic) if you apply rows of thin beads of it.
65% or even 60% humidity is a lot better than the 40%, 30%, and even 20% most iguana have to live in. Try reducing it to 65% and see what happens. Then reduce it to 60% if you have to.
The cool human temperature of the house conducts through the plastic and flows down the inside face. In homes, heat registers are located under windows to stir up the flowing drafts of cold air. I think you can put small fans across the bottom of the plastic front to blow air up, which hopefully will stir the 1/4 inch layer of humid air layer against it, preventing or reducing the condensation, at the same time as re-distributing the humid air that wants to condense out onto the glass. I think that is worth a try. Too much wind will cool t3e iguana.
Since heated air has lower relative humidity, think about this reasoning: Applying the habitat's heat along the bottom of the front will cause warm air to rise along the inside surface of the glass, hopefully eliminating the condensation. The heat will rise to the upper part of the hab and heat your iguana well. It will set up a slow air circulation, with warm air rising along the front, slowly re-cooling at the top, and then flowing back down to be re-warmed. If you give your ig enough perches throughout the hab, he is well able to find the spot he considers to be his most comfortable. Still provide a heat zone, near the top, which he can bask in. As you know, he is genetically programmed to regulate his temperature by moving between the warmest spot and the cool zones throughout the day. A row of 10- or 15-watt light bulbs across the width of the hab will prevent hot spots that can injure your ig. You would have to test the surface temperature of whatever grid you cap the row of lights with, non-metallic is best, because your ig will surely lay on it.
The next level is to replace the front with dual-glazed glass. But at 75% humidity, even that may get too much condensation. Triple glazing is available. But reducing to 60 or 65% may solve this problem.
I think if you do some of these things, you can remove the ventilation fans, which only remove the air which you have to mechanically condition with warmth and humidity. Why throw it away? It will produce a more stable system. 3 each, 1/4 inch holes at the bottom and top will provide plenty of gas exchange.
Your iguana is very lucky to have such a dedicated owner.