Every year seems more people learn of this spot so it does get busy starting in July, which is to early if you're looking to see Glacier NP. We try to get there end of August and have never had a problem finding a place but you will be the with a dozen or more others. In the last 4 years never pulled in and not found a spot. Around the loop gets taken 1st so you may have to park out in the center. Not as desirable, kind of lumpy and tall grass hiding things.
We visited for 5 days on July 4th weekend 2023. There were around 15 rigs and not much turnover. We found a spot for our 38ft motorhome with no problem on a Sunday morning. Thursday morning was the emptiest.