There are many threads on this topic, expressing a range of opinions.
My opinion is that cell boosters such as Weboost devices are just short of a scam. Then only help under very narrow conditions. Most of the value comes from having an antenna outside of the metal box of your van. A much better way to do this is to get a mobile hotspot that is capable of accepting external MiMo antennas, and to mount a good MiMo antenna on your roof. MiMo is vastly more effective than attempts to amplify a noisy cell signal. I have described the reasons for this elsewhere.
There are folks who believe in cell repeaters and have reported good results, and I'm sure they will contribute. But, in my experience with a wide range of such devices, they are snake oil.
Formerly: 2005 Airstream Interstate (Sprinter 2500 T1N)
Now!: 2014 Great West Vans Legend SE (Sprinter 3500 NCV3 I4)