When I had Sportsmobile North outfit my van they told me there wouldn't be enough room to install solar on my roof because I had already elected to have them install a MaxxAir fan and a roof AC unit. It wasn't an issue because I had a second alternator installed to quickly recharge the batteries and had ordered my Sprinter with the adjustable high idle feature. This allowed me to idle the van at a high enough rpm to let the second alternator quickly charge my house batteries if I wasn't going to be driving anywhere.
I did have them add a solar power port on the outside of the van so I could use a set of portable solar panels for those rare instances where I boondocked in the same place for multiple days and yet didn't want to idle the van to charge the batteries.
Since I have the portable solar panels I decided to add a second solar power port INSIDE my van. This allows me to set up my portable solar panels on my dash and plug them into this new port to trickle charge the house batteries. This is proving to be a great way to offset the small power draws I have when I park the van at home. I live in a condo complex and have to park my van in a parking lot where I don't have access to A/C power to keep the van's batteries topped off.
Just a quick mod to get some extra use out of the portable solar panels I already have.