Delegating somebody to vote on behalf of others can have two benefits:  People are able to vote who otherwise wouldn't be able to vote,  The person casting the vote on behalf of somebody else can also vote themselves.
This is a great concept! Not only could voting vans be deployed to hospitals or residential areas, they could also be valuable if sent to business parks where people on busy schedules could come out to vote during coffee or lunch breaks. In this fashion, voting vans would serve a similar role to food trucks by providing a convenient means for people with busy schedules. Additionally, voting usually occurs during business hours and a business park during business hours will have lots of people.
Voting vans could park in a central location of the business park and have the people come to them or they could travel between the parking lots of several companies throughout the election day. The difficulty of the former is the people on the periphery of the business park may not be motivated to travel the distance to vote. The difficulty of the latter is figuring out where the voting van is when you want to vote, but this could be mitigated via Twitter or information posted online.
The same concept can be used in assisting people to register to vote before election day therefore familiarizing them with the voting van process for the actual election day.