UGH, I can sympathize - we are cancelling our weekend trip too to Delaware Seashore State Park.  It was to be our last 'long' weekend before the boys and I start school (DS's & I would leave early Friday morning and come home on Monday, with DH commuting to and from work on Friday & Monday respectively (his workplace is an hour closer to the campground than our house).  We also initially thought we could enjoy Saturday and just leave that night or before the rain Sunday, but right now that seems impossible.

I feel your pain, we were really looking forward to this.  Then again, I've already had to replace an awning due to un-forecasted gale-force winds at that same park, so it's better to be safe than sorry (though that won't make anyone jump for joy at having to cancel a trip).

Maybe you could plan an extra-relaxed weekend (since you would more or less be on vacation anyway) at home? When my DS's were little, they enjoyed indoor camping (getting out their sleeping bags and sleeping in the living room under a tent improvised made of sheets after watching a movie or playing board games, having us cook 'cookout food' (hot dogs, hamburgers, etc.) in the living room on an electric griddle, telling bedtime stories by flashlight/lantern).  This usually tired them out and DH and I could get some extra 'sleep in' time 😉 the next morning (if we didn't wind up sleeping out on the living room floor with the boys).  I admit that it's hard to be at home and not want to undertake a project on a rainy weekend; getting into the 'stay-cation' mode can be hard, but it can give you lots of happy memories.

Now that DS's are 14 & 16, they still enjoy rainy days (when they aren't busy with homework or school), but the focus has shifted - they enjoy sleeping in, board games (though it's now Backgammon and Texas-Hold-Em rather than Sorry and Monopoly), video game score challenges (DH and I only play 'old school' games like the Sonic series, DigDug, Tetris, etc.) movies (anything with Chris Farley or Will Farrell is something all of us can enjoy), and alternating between snacking and large meals that, because of their preparation time, are usually reserved only for holidays (gumbo, turkey dinners, pot roast, shrimp etouffee, homemade pierogy, chicken soup).  They're pretty disappointed that we probably won't be going this weekend (our oldest is into photography and has made a couple of 'suggestions' that it would be 'cool' to photograph a hurricane at the shore; the youngest insists that the surf fishing will be extra productive because the storm will drive the fish shoreward) but DH and I are trying to make the best of it. 

It stinks to have to cancel something that you were really looking forward to; it sounds like you really had a wonderful weekend planned.  Then again, it's also nice to have nothing planned and just relax at home (provided that you can overcome the 'chore/project urge').  Maybe since you're trying to sell your house, you could make it like a 'last hurrah'?

Best of luck - I truly sympathize!