Treat dense jungle areas as buildings. You can only attack as per the house to house attack rules, or you can fire into, but the defender is in hard cover.

Vehicles ( all ) can only move on road.

Jungle is not all thick dense vegetation. As well as the dense and light jungle ( I have been to the jungle in the Yucatan / Mexico on the Guatemalan border -- which was light/medium jungle and it didn't really slow us down that much. The only thing that delayed us in our jungle trek was the moaning women -- oh the mosquitos, oh the snakes, oh the spiders, oh the ants etc, etc.

There are large clearings, tracks, paddy fields ( flooded and dry ), palm /coconut /rubber tree plantations, streams, rivers, swamps, Kunai (elephant grass), villages, and roads. The challenge is to get a balance, and to know what terrain is what.

I would also allow that certain troops ( in the same vein we discussed mountain troops not paying a movement penalty in mountains ) was that jungle specialists have non penalised movement. I would allow all Japanese, Burma rifles and other indig's types , Chindits, Gurkhas, and Merrill Marauders free movement in light /dense jungle.