In case anyone with an E-series was wondering, a $45 Tacoma snorkel will work to get cleaner air
Took a risk based on some rough measurements, and this cheap Toyota Tacoma snorkel from eBay fits pretty well. It's not 100% perfect, but it'll get the job done. One 3.5" hole, three 3/8" mounting holes in the fender, and some 3M VHB tape on the a-pillar is all it takes to mount up.
I got tired of swarms of bugs clogging up my air filter, so I searched for snorkels to get cleaner air for my 2003 E350. There are no reasonably priced off the shelf options available, and I don't like the DIY/PVC look. This taco snorkel kit was cheap ($45), and the dimensions work well a Ford van. The snorkel has a 3" diameter in/outlet, which is the same as the OEM airbox diameter (5.4 v8). I had to get an additional $15 section of flexible tubing to connect the snorkel to the airbox via an opening in the inner fender.
Not pictured is a pre-filter that spins some debris out of the air before it even hits the air filter. This keeps bugs, sand, and fine dust out of the intake, extending the life of the filter. The basic ram air intake in the pic can be covered with a pre-filter "sock" to keep larger debris, like bugs, out as well. #lifestyle source