Years ago I made some enclosures for my Electrovoice 18" subs and they look very similar to what you show. The ports are across the front at the bottom and the rest is sealed. I haven't used them for years, but they would rattle the entire house when turned up and the house is on a 5" concrete slab.
I don't know what you mean by having them done right. It's all about the dimensions of the port and even that was not super critical. I think they were called "ducted ports", but it was a long time ago.
Here's what I found online:
I don't know if starting over is necessary. The construction methods I used were 3/4" particle board and lots of glue. I covered them with a satin black laminate. I also made a set of 15" EV midrange enclosures which were the same foot print and they stacked on the 18's with rubber isolation pads under them. On top of each stack were 3 hypersonic University T-50 tweeters. I used 6 AMPs to drive them all, 4 - 100 watt and a dual channel 200 watt, mild by today's standards, but way powerful enough to drive bass reflex speakers at that time. Tweeters don't take that much power.
Today's, well yesterday's "powered" subs with built in AMPs work very well and Radio Shack made some great ones for the price. I have about 4 of them around the house and in the shop. I found a single 100 watt AMP worked just fine with the small die cast remotes for the midrange, hung on the walls or placed on furniture and took up much less space that the ducted port enclosures, which was critical in the shop. Bass notes are non-directional of course.
Kinda like this one:
Now with my hearing loss of high frequencies, I can't appreciate the beautiful sounds of days past. Getting old means getting wiser, but losing other capabilities, not such a great trade off in my opinion. I'd rather be a little more stupid and still hear well. DUH. <img src="http://www.woodworkingtalk.com/images/WoodworkingTalk_2016/smilies/tango_face_plain.png" border="0" alt="" title="Serious" class="inlineimg" />
To answer your question, try out the enclosures you have before starting over. I think you will find them satisfactory, unless the wood joints fly apart. You can always install glue blocks on the inside corners where the joints meet IF they are not already there, assuming the back is removable OR if you can access them from the opening in the front. They can't harm anything and will increase the structure immensely.
I don't know where you got your plans but I recall using some from Electro Voice for mine. Maybe from a source listed here:
BEWARE of the link Best 76 Plans, it's a spammer named Ted's plans. DO NOT Click that link!