Just some info on fans. 3, 5 and 7 bladed fans tend to run quieter and most DC fans like on a power supply for desktop PC's run much faster than 220V AC driven fans. One can go the inverter route as Geert mentioned but the non pure sine wave inverters give exstra noise due to the modified sine wave.
A quality pure sine wave inverter like the Cotek S150 or SK150 could cost about R1650 to power a 220V AC fan. One can also go for the USB fans as mentioned above. Available on bidorbuy at R59. Up to 8 of these fans can be powered from a 12V x 2A lighter USB charger. These chargers with 2 outputs go for R40 at a China Mall. Further one can also power the fans from a power bank. Using a 8000mAh-10 000mAh power bank should power 2 fans for about 8 hours. These power banks can then be charged during the day. This is a low cost solution.
Just as Peter indicated above I use one of these very cheap lights from a power bank up to 30 hours before recharging to light up my keyboard at night. These lights do use about half the power the fan above would use.
Got a small fan from GAME that does a fine job. Three speed selector.
My caravan (Sensation Maia) had a aircon in. We hardly used it and mostly made use of an electric fan.
I have searched for a proper (Good looking) 12V fan for about 3 years and never could find one. The ones I really liked I saw in caravans on a aussie website not available in SA.
Midas has a 12V model but it is too ruff and ready for my liking. And it makes a lot of noise while running.
Only other option was to buy a recharge-able one (they look better) and convert it to a 12V permanent installation. Had to sell the van before I could really get to it.
You have a off road van, so you could be less finicky about how the van looks.
Another option is a car radiator van with a motor speed control. (Like dimming a light).
If you mount it in an aluminum frame it could look beter than the one available from Midas and it would be much quieter.
Look at this one at Clicks.
Ek het hierdie waaiers by karavaan skou gesien gedurende Februarie by Gallagher Estate. Die battery kan jy op verskillende items gebruik. Ek het belang gestel in boor, blower en waaier. Toe ek by skou wou koop is waaier uit voorraad. Ek het sedert daai tyd tot nou kortkort gaan hoor by hul winkels....heeltyd veskoning dis oppad, dit lê in hawe. Die blower is ook nou al meer as 3 maande uit voorraad. Afgelope week was hulle by Kragdag skou gewees....het niks meer in voorraad nie, net chargers. Ek wil koop, maar wil weet ek gaan alles kry, maar lyk nie of dit gaan gebeur nie. Sal ook maar na iets anders begin loer....