Help with bonding plan??

Hi, I am planning on bonding my two buns in a few weeks time and I just wanted to put my plans out there so anyone with experience can let me know if it sounds good or not!!!

My boy Bubs (3 yrs old and neutered at 7 months) lives downstairs in the study but has full run of downstairs when he's out playing. He has also been up the stairs and in a few rooms upstairs on occasion.

My girl Dolly is a newer addition, she's adopted, 2 years old and we had her spayed 2 weeks ago. She lives upstairs in my bedroom and hasn't been anywhere else yet.*

We have lived with them separately like this for about a month and a half now, so they have probably smelt each other on us but have never actually seen each other.

My plan is to get a large cardboard box and put them both in it, take them on a car ride around the block and see their initial reaction. Then, if all is looking ok and no fighting in the car I will take them both up into the (converted) attic where neither have been before. Up there I will have a small play pen set up with water, hay, fresh greens and a towel (it's laminate flooring). I've read about also having a spare towel and thick gloves on as well as a*
Spray water bottle to hand so I'll have all that.*

I have no plans that weekend so I'm hoping to just stay with them up there all day and possibly all night, although I know this is probably wishful thinking!

My main problem is where to go from here, do I also have a new cage set up ready in the attic for them to go into together should they get on, or do I also bring both their old cages up there incase they don't but so that it all stays in neutral territory? Or does bringing old cages into it mean it's not neutral anymore and I should just take them back to their old separate zones 'til the next days session?

Also once it seems they are getting on am I ok to move the shared cage down to Bubs room? Obviously no longer neutral territory could this upset the bond?

I know it's really hard to plan until you see the initial reaction but I really don't want to make any mistakes on my part if possible!

Thanks for help in advance!

The playpen in the attic sounds good although I would recommend a waterproof sheet on the floor and then fleece/sheets on top. Besides hay don't put anything else in until you see how the buns are behaving with each other. You won't need the car trip if things go well in the playpen.
If they settle well with each other, you can neutralise all the places Bubs has been with a vinegar/water solution (floors, furniture, toys) and gradually increase the space they have.
I even moved furniture around so it wasn't the same routes they knew

Once the major chasing etc is over you can put in the water bowl (I used a heavy pyrex dish) and give food.

Don't try moving them too early. Mine didn't get more space until they were lying or eating side by side with no upset and I saw grooming
Good luck

Great, thank you, I will try skipping the car journey part and just go straight to the pen and will definitely put down soft and waterproof layers on the floor too.

I'm thinking if I then have a new cage set up in the attic they can eventually move into there together, continue living in the attic until they are fully bonded at which point I'll move them both back down to bubs area. Not sure about cleaning the whole downstairs with vinegar and water, but I'll do my best and will see if I can have a move around.

Are there some bonds that just go well? I only seem to hear about troublesome ones!!! I'm worried because my buck can be a little unpredictably angry sometimes! He'll go for months being the cutest loveliest boy and then all of a sudden you'll be stroking him and he'll spin and sink his teeth in! I just hope he doesn't do this to Dolly!