Hi 22y. We have a 7.2 metre caravan and the one D2 Eberspacher is more than up to the task. I cannot see that you would need two if you have two outlets to the heater (duct one down to the back - well insulated). Check Trademe #874730222 and plenty of others at present. Cheers.
Derb. 2017 Colorado LTZ 4 x 4 Auto. 2014 Southern Star 720 and 1980 Zephette 340. 2 x 100 a/h AGM. 3 x 150w solar. Ctek D250S-Dual controller/MXS15 charger.172L fresh/grey. Diesel heat. RMD8555 fridge.