I have been searching the net to find recommendations for trailer flooring, in particular what thickness board, cannot find anything so thought that I am bound to get some good advice here.

I restored the trailer back in 2012 but I never got around to replacing the floor and thought it would last a couple of years so I am amazed its lasted till now.
Its 6' x 4' has a central spine and cross members at 18" intervals, see picture.
I want to use a good quality phenolic coated board but at what thickness? I'm thinking 9mm but should I use 12mm?. It just gets used for general duties such as trips to the tip, the heaviest items its ever been used for is a medium sized mobility scooter and a 90cm range cooker.

Alternatively can I use Aluminium checker sheet? if so what thickness

Click image to enlarge

Aluminium chequerplate min. 6mm

What about formply (used for forming up concrete)- like this: https://www.falconpp.co.uk/products/plywood/formwork-plywood/ Ron B. VK2OTC
2004 L322 V8 Auto
2007 Yamaha XJR1300
Previous: 1983, 1986 RRC; 1995, 1996 P38A; 1995 Disco1; 1984 V8 County 110; Series IIA

I did a similar project many years ago and used 18mm marine ply. It hauled loads of building rubble whilst I renovated 2 houses we had. It was better the chequer plate in my view, easer to run a shovel along, sweep, slide sacks etc. BMW i3 Electric Car
2012 Full Fat RR 4.4 TDV8 (now gone)
2006 VW Touareg 3.0 TDi V6

Most builders yards do a board especially for trailer bases it’s like a bitumen infused chipboard with a rubberised non slip surface very tough and for your trailer prob cost £40-£60 of the top of my head I’ll have a look for the receipt btw I’d go 18mm min 2012 Range Rover Westminster 4.4 TDV8
2006 Discovery 3 HSE 260k miles and still going strong with a new owner

Looking at the floor framing 12mm marine plywood would be more than adequate. Personally I would treat the underside of the board with waxoyl before fitting.

At least 12mm I would say, and coated Phenloic board. Should last a while then, it’s the sort that most trailer manufacturers fit from the factory. Had our Indespension done a couple of years back before it wandered off..... There is nothing that can't be fixed with a hammer😜😜
FFRR 4.4 SDV8 Autobiography Santorini Black.
Fiat 500x 1.4 multiair Lounge 2015
2010 LR D4 Commercial 2.7 TDV6

Phenolic ply - avoid aluminium chequerplate like the proverbial plague as it’s filthy, hard to clean, noisy and slippery when wet.

The alternative is to use thermoplastic honeycomb panels - they are now using this for body’s for the various home delivery vans as it’s lightweight but strong as anything... http://www.coretexgroup.co.uk/6.html although others are available if you search for suppliers.

Thanks every one for your help and sorry for the lateness of my reply.

I have decided to go with 12mm Phenolic ply based on advice here and elsewhere .

David Range Rover 4.2 Supercharged 2006
Ford Focus EcoBoost 1.5 2017
MG TF 2003

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Land Rover Discovery 2
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MG Midget 1974 - Concours