Disclaimer: This page contains various affiliate links that provide a small kickback to me, at no additional cost to you.
Note: Actually got upgraded for free to the M2D4R Heater, $1995, but spent $1,640
https://www.youtube.com/watch?v=aFzZbWv8ZhE&ab_channel=Miller'sRV
truma heater combi
https://www.youtube.com/watch?v=zCjygu0ygKE&ab_channel=GregVirgoe
https://esparparts.com/espar-s2d2l-commercial-mercedes-sprinter-p-25588.html
https://esparparts.com/easystart-pro-p-25533.html?affiliate_banner_id=1&ref=17
https://www.heatso.com/webasto-air-top-evo-40-12v-diesel-heater-smartemp-3-0-kit-high-altitude/?sku=5014149A
https://shop.cummins.com/CSSNAStore/s/product/a2w4N000003sQzIQAU/webasto-air-top-evo-55-diesel-kit-12v-5011177b?store=EN&srsltid=AfmBOooWaE4lCka2yHDufaZ7xIyT3hFLHuZgM36tCKOcOLDoXIRX89undkU