Yuri,
Im not sure that you will have a whole lot of success using a Paltier. The temperature difference is key in its working, and if your generator is under the hood with all of the heat in that compartment, you will only be able to produce a little energy.
If you use that bit of energy to circulate air, a better idea might be to find airflow from an outside source such as a bit of captured moving air from outside the moving vehicle.
If you are trying to circulate water, then you may only be able to move a very small ammount of it at a time, and to a very short distance.
An efficient active cooling system for the generator is sort of the holy grail. I have spent alot of time trying to nail the best temperatures, pressure, electrolyte solution ammount, electrolyte mixture, number of plates, and also the type of plate cells.
Its relatively wasy to get the ammount of HHO production, its just what to do about temperature and other things that affect efficiency.
All in all let me know how the peltier works for you, I am VERY interested. I only theorize about the outcome because I havent tried it yet, but I may do so if there is any good results found by others.
Thanks in advance
"You don't always have to know ALL the answers, but you do need to know where to find them."