On behalf of the entire Campendium community: thank you for keeping the RV on your profile up to date! Sharing your RV type and length is useful for others in the Campendium community who might be looking to see if the place you stayed will also be accessible or pleasant for them.
You can update your RV make, model, and length from your profile page. Once you're on your profile simply tap 'Profile' on the right then scroll down to the 'What are you camping in?' section:
Don't worry if you need to update from an RV you previously traveled in! RV details stick to a review based on the RV you have on your profile at the time you post your review.
So, the reviews you posted with your old rig will still show the length and details for your old rig. Any reviews you post after updating your RV will show the length and details of the new RV. (Congrats on your new RV, by the way!)