i recommend camping at the CG at the north end of the park on the west side of mount Lassen, near lassen ? lake
take warm clothes temps got down to freezing at night in mid july
there was snow on the mountain top when i took the kids there in july many years ago, the Hike to the top over 8200ft can be a work out, but trail was in good shape when i was there (and much younger)
i don't think anybody will get to play in snow this year
be sure to visit Bumpus Hell and go south to Lava Beds Nat Moumnent
and explore the lava tube tunnels