TRIM then LOWER then SUBSTITUTE formula needed

I'm trying to replace spaces with plus signs and make the result lowercase.

So <space>Pittsburgh Steelers would be pittsburgh+steelers or Pittsburgh Steelers<space> would be pittsburgh+steelers or <space>Pittsburgh Steelers<space> would be pittsburgh+steelers

Any space beginning or end is removed, then it is made lowercase, then the spaces are made plus signs.

I'm trying this =TRIM(LOWER(SUBSTITUTE(BI1," ","+")))

But it is replacing the spaces with plus signs before trimming so I'm getting +pittsburgh+steelers with a + in front.

How can I get it to trim first... then lowercase... then sub remaining spaces with +? or lowercase, trim, sub whatever. The trim must happen before the sub is the key.

Thanks!

Perfect Martin ! Thank you so much!