Book the first night at St. Vrain State Park before you book the van. It's a chain of gravel ponds near Firestone, out on the plains east of Longmont, where you fish for bass, put a kayak in the water, and watch Longs Peak stand on the western skyline over the cottonwoods. Every site is reservation-only through cpwshop.com, six months out or the morning you drive over, and camping stays open year-round, so the site goes in the calendar first and the van second. The campsite fee doesn't cover the gate either, and the vehicle needs a Colorado state-parks pass on top of it.
If the ponds are full for the weekend you want, the Boulder County Fairgrounds campground on Nelson Road takes first-come RVs, no reservations.
Booking a pond loop at St. Vrain
The choice is the north loops or the south, both strung along the ponds at the park's eastern end. North puts you on electric sites under more cottonwood shade, with the shower building and the dump close by. South trades the shade for a water and dump drain right at the pad and pull-throughs 50 feet or longer, which is what a bigger rig needs. Electric sites run $36 a night and the deluxe sites $41 as of August 2026, per the park brochure.
Summer afternoons on the plains floor run hot, with July highs near 91 F in the NOAA 1991-2020 normals and near-daily storms, so those hookups earn their keep. In a hard freeze the park may shut the water hydrants while the sites stay open. If you're weighing a motorhome for the length or the extra beds, you can price one against a van on RV rentals in Longmont.
Rocky Mountain National Park, west through Lyons
Rocky Mountain National Park runs up the Estes corridor, west on US-36 through Lyons. The whole overnight up there is laid out on the Denver campervan page.
Boulder's canyons and open space
Boulder's Flatirons, Eldorado Canyon, and the Indian Peaks are day-hikes to the southwest. Camping is barred on Boulder County open space, so you either drive back to the ponds for the night or set a Boulder base with campervans in Boulder.