I will answer with how I pin baste -
(I make sure the top and backing are pressed before starting this) (I also wash the fabrics before cutting them - and the batting - if washable - before using it. But that's a whole another topic)
and
I also have a fairly long table - 96 x 38 inches
I do center the backing on the table and smooth it so there are no wrinkles in it - but not pulled tight - I do tape this middle section to the table so it does not slide around.
I then weight the sides down with yardsticks, or curtain rods - I just fold some fabric over them and encase them - this provides enough weight to keep the backing from rumpling - and holds it slightly taut.
Then I layer the batting and top - this is where I spend a LOT of time making sure that it is lined up "square" - there is fabric hanging over both sides of the table - but what is ON the table it "right"
I pin as far as I can go - then I slide everything one way or the other as you do - I do retape the backing to the table - but don't pull it drum tight.
So far - I have not had wrinkles on the back.
I did learn that pullilng the back drum tight was not a good idea for me - because when the fabric was released - then the top was bunched up - not much - but a little bit.