There are no RV parks real close to Boston. You could check out the Boston Minuteman Campground in Littleton, MA. Gets good ratings and the price is about $45/night for 50 amp. Depending on where in Boston your conference is, it's around 45 minutes down route 2.
If you decide it's OK to drive that far to your conference, look at hotels in the suburbs. They are a lot cheaper than Boston prices. Especially when you add all the Boston city taxes.
As an example the Red Roof in Salem, NH (closer then Littleton, MA) is $80/night.
2007 Newmar Essex 45'
2006 Honda CR-V and 2005 Chevy Silverado 1500
2004 HD Electra Glide Ultra Classic
2006 HD Heritage Softail Classic
Overbilt Lift
I's suggest Minuteman, Normandy Farms, Pinewood Lodge.
All on outskirts of Boston.
Take a look here: Northeast campground reviews
Our Portable Summer Cottage II :2000 GBM LANDAU 2905 F53 w/ Sumitomo ST718's, Bilstein's, Steer-Safe, UltraTrac
& Aventa II pulling a 97TJ - Click for Pics & Mods The Crew: Lovely Wife, Daughters (14/11), Crumpet the Springer LIFE IS GOOD!
Another issue you are going to run into is the height of your truck. Most of the hotel and general parking garages aren't tall enough for high profile vehicles. I'd suggest contacting the facility the conference is being held at to determine whether or not the truck will fit.