So far this is what I have done:

1) Installed the module: Settings->Modules, search webkit, install report_webkit

2) Add Webkit Logo: Settings->Technical->Webkit Logos
Create and add custom png logo

3) Alter Webkit Headers/Footers: Settings->Technical->Webkit Headers/Footers 
Change to Letter Format

4) Edit Company Data: Settings->Company Logo
Webkit tab: Add logo, Add Headers: select Base Sample

5) Change Invoice to webkit: Settings->Technical->Actions->Reports, Search for Invoices
Edit
Enter "webkit" into Report Type field (originally pdf)
Deselect "Add RML Header"
Select Webkit Tab (appears after Report Type is changed)
Set Webkit Header to: Base Sample

[After my first few rounds with the the print issue I also coppied the demo Mako webkit example into the "Webkit Template (used if Report File is not found)" field, and I also enabled webkit debug]

Going to invoice and hitting print now throws up:

OpenERP Client Error

Uncaught SyntaxError: Unexpected end of input

Setting the invoice report back to pdf returns functionality.

Now, I do not know if the problem is whether wkhtmltopdf is missconfigured on the SaaS server, its PATH is not set on the host, or if I am doing something else wrong. Would really appreciate any input or ideas on solving this as custom output is needed and the SaaS documents do not seem to exist for webkit.