Lay the frame on it's side.

Protect the cylinder and press feet so that when you weld, spatter won't stick. You could use some piece of metal or a nonflammable cloth.

On the inside, bottom edge, weld the interior of the spacer inwards as far as you can. This should be an inch or more. Do this in all 4 corners accessable from this side of the frame. See the photo.

Weld the top 100%, and grind it flush.

Flip over the frame.

Weld this side as you did the other side, also welding inside the spacers.